Process of cementation



Patented Feb. 23, 1937 UNITED STATES PATENT OFFICE PROCESS OFCEMENTATION Harry K. Ihrig, Milwaukee, Wis., assignor to Globe SteelTubes 00., Milwaukee, Wis., a cor- No Drawing.

, Serial No. 8,704

29 Claims. (Cl. 148-131) This invention relates to a process ofcementation of metals, particularly iron and steel, to render suchmetals non-corrosive and acid-resistant.

cementation of metals with carbon and other elements is well known inthe art. The use of phosphorus and certain phosphorus compounds such asphosphine is also old. Alloys of iron and phosphorus and copper-tinphosphorus bronzes are also old in the art. Prior methods for theintroduction of phosphorus into metals by cementation, however, haveemployed either the element phosphorus alone, or volatile phosphoruscompounds such as phosphine. Ordinary yellow phosphorus is a verydangerous substance to handle. It is very poisonous and spontaneouslycombustible in air and to preserve it it must be stored under water.Phosphine or hydrogen phosphide is likewise very poisonous andspontaneously inflammable. Furthermore, the cases formed in the basemetal under these prior methods, while somewhat resistant to corrosivesubstances, are much less resistant than those of the process about tobe described. The use of phosphorus in a coating metal, which in thecase of copper and tin phosphide coatings gives a very acid resistingcoating, has the disadvantage of being very brittle. Being a coating andnot an integral part of the metal itself, it often cracks and spalls01f, exposing the base metal to corrosion.

According to the present invention, phosphorus impregnation orcementation of the base metal is obtained wtih non-poisonous,non-inflammable, relatively inert, readily available, and inexpensivecompounds of phosphorus, and the phos phorus is readily absorbed by theiron or steel to form a phosphorus case of appreciable depth, impartingto the resultant product highly desirable and advantageouscharacteristics such as superior and lasting corrosion-resistingproperties. It is further contemplated according to the presentinvention to impregnate the iron or steel with copper either before,after, or during the impregnating of such metal with phosphorus to thusimpart to the metal high acid-resisting properties in addition to thecorrosion-resisting properties imparted thereto by the absorption ofphosphorus.

I have discovered that when iron or steel articles are heated in contactwith oxygen compounds of phosphorus such as phosphorus pentoxide, sodiummetaphosphate or other relatively cheap phosphorus compounds such ascertain fertilizer compounds, slags and ores, the iron reduces the oxideof phosphorus and the phosphorus formed in situ is readily absorbed bythe iron to form a phosphorus case. This reaction may be speeded up bythe use of certain catalysts such as finely divided nickel. It may alsobe speeded up by an excess of iron. Thus, if an iron container is used,the reaction is catalyzed by the container.

The case produced by the absorption of phosphorus by the iron in thisprocess, while resistant to atmospheric exposure and other mildcorrosive agents, is not highly resistant to acids such as sulphuricacid. If, however, the case contains copper as well as phosphorus, itbecomes highly resistant to sulphuric and other acids as well as tocorrosion. The copper may be introduced simultaneously with thephosphorus or before or after the phosphorizing treatment. Anyconvenient method may be used, such as the treatment of the metal withcopper chloride or with organic salts of copper at high temperatures asdescribed and claimed, for instance, in my copending application SerialNo. 732,305, filed June 25, 1934. In the simultaneous treatment, thecopper salts may be mixed with the phosphorus compounds and then heated.Another method equally effective is to treat a copper steel withphosphorus compounds resulting in a case containing both phosphorus andcopper.

As a laboratory example of the first method of cementation, a piece oflow carbon seamless tube was packed in a larger steel tube closed at oneend, with a mixture of 10 grams of phosphorus pentoxide, 10 grams offinely divided silica, and 3 grams of copper chloride. This was heatedto a temperature between 1600 F. and 1900 F. in an electric furnace andmaintained at such temperture for four hours with nitrogen gas runninginto the top of the container tube to replace the air. After cooling,the sample was found to have a copper colored surface and, on immersinga severed section of the tube in dilute sulphuric acid for twenty-fourhours, the core was attacked by the acid while the case was resistant.

I have also discovered that in lieu of the chloride in the aboveexample, in the use of which there is some danger of attack on thesteel, the oxides of copper (either cuprous or cupric) may be used veryefiectively for impregnating the base metal with copper. The ironreduces the copper oxide at the high temperatures used and the copper inthe nascent state is immediately absorbed by the base metal. Thiscombination or use of two oxides-phosphorus and copper-to impregnate abase metal by cementation with the elements phosphorus and copper isbelieved to be entirely new in the art and to possess heretoforeunrealized advantages in application, effectiveness and resultsobtained. Thus the following is an example of this modification of thefirst method above referred to as practiced in a pilot plant now inoperation:

35 pounds of dry sand, 1 pound of phosphorus pentoxide and 1 ounce ofcuprous oxide were placed in a substantially air-tight iron drum whichwas revolved slowly in a furnace. Two five-foot tubes were placed insidethe drum with the above mixture. Nitrogen gas was introduced into oneend of the drum and escaped through a water seal at the other end. Thedrum was started revolving and the furnace was brought up slowly to 1810F. and held at this temperature for approximately four hours. It wasthen cooled down to room temperature and the tubes removed. They werefound to have a smooth gun metal colored surface, and upon immersing asevered section of one of the tubes in dilute sulfuric acid fortwenty-four hours, the core was attacked by the acid while the case wasresistant.

As a laboratory example of the second method of cementation abovereferred to, a bar of low carbon 2% copper steel was packed in 3 gramsof phosphorus pentoxide, 10 grams of finely divided silica, and 2 gramsof nickel oxalate in a silica tube. a temperature between 1600 F. and1900" F. in an electric furnace with nitrogen gas passing through thecontainer to replace the air. The sample after cooling showed aresistant case on being immersed in a 10% solution of sulfuric acid fortwenty-four hours. The nickel oxalate included in this example functionsas a catalyst and facilitates the reaction, permitting the same to occurat relatively lower temperatures when it is present in the mixture.Furthermore, it appears that the decomposition products of the nickeloxalate assist in the reduction of the phosphorus pentoxide.

In all the above examples, photomicrographs of the samples revealedsubstantial impregnation in the form of a case with the copper andphosphorus thoroughly and permanently penetrated into and combined andalloyed with the base metal of the piece. The result is a truecementation and not a mere coating. Crushing the impregated tube showsthe case to be very ductile and no spalling of the case takes place evenunder extreme distortion. The alloy produced by my process may be termeda cementation alloy as distinguished from an alloy produced by fusion.

One purpose of the finely divided silica in the mixture is to dilute thephosphorus compounds, but it is believed that the presence of the silicaalso aids in the reaction by facilitating the reduction of the P205. Theequilibrium may be expressed as follows:

The silica and the catalyst may be used over and over by enrichment atthe beginning of each run with the phosphorus compounds.

One identifying characteristic of the invention is the production of aphosphorus case in iron or steel by the heating of such metal in contactwith oxygen compounds of phosphorus into which case, if desired, coppermay also be introduced by copperizing a non-copper steel before, after,or simultaneously with, the phosphorizing process. The same result maybe attained by phosphorizing a copper steel. The process and theresultant article are believed to be new This was heated for four hoursat in the art and to represent a decided advance therein. The use offree phosphorus and the dangerous compounds of phosphorus heretoforeemployed is avoided. The penetration is posi tive and substantial andthe case is more ductile and acid and corrosion-resistant than thoseproduced according to prior practices.

In practicing the invention, other or additional inert or reducingagents may be employed such as carbon, hydrogen or city gas. I havefound that by the use of finely divided carbon, the reaction can be madeto take place at lower temperatures and that carburizing does not occurif an atmosphere of nitrogen is employed. I have also found that by theuse of city gas instead of nitrogen as an atmosphere, a phosphide caseis obtained, but carbon is also absorbed. By mixing nitrogen with citygas, the carburizing action is cut down, while the reducing action ofthe city gas speeds up the phosphorizing reaction, especially at lowertemperatures.

I claim:

1. The process of impregnating with phosphorus by cementation a metalcapable of alloying with phosphorus which consists in heating the metalunder non-oxidizing conditions in contact with an oxygen compound ofphosphorus, at temperatures suflicient to decompose said phosphoruscompound.

2. The process of impregnating with phosphorus and copper by cementationa metal capable of alloying with phosphorus and copper which consists inheating the metal under nonoxidizing conditions in contact with anoxygen compound of phosphorus and a copper salt at temperaturessuflicient to decompose said phosphorus and copper compounds.

3. The process of impregnating with phosphorus and copper by cementationa metal capable of alloying with phosphorus and copper which consists inheating the metal under nonoxidizing conditions in contact with anoxygen compound of phosphorus at a temperature sufiicient to decomposethe phosphorus compound, and thereafter heating the metal under the sameconditions in contact with a copper salt at temperatures sufiicient todecompose said copper salt.

4. The process of impregnating with phosphorus and copper by cementationa metal capable of alloying with phosphorus and copper which consists inheating the metal under nonoxidizing conditions in contact with anoxygen compound of phosphorus at a temperature suflicient to decomposethe phosphorus compound, and thereafter or prior thereto orsimultaneously therewith heating said metal under the same conditions incontact with a copper salt at a temperature sufficient to decompose thecopper salt.

5. The process of impregnating copper steel with phosphorus bycementation which consists in heating the copper steel undernon-oxidizing conditions in contact with an oxygen compound ofphosphorus at temperatures sufficient to decompose the phosphoruscompound.

6. The process of impregnating iron or steel with phosphorus and copperby cementation which consists in heating said metal under nonoxidizingconditions in contact with a mixture of phosphorus pentoxide, silica,and a salt of copper at temperatures sufiicient to decompose thephosphorus and copper compound.

7. The process of impregnating iron or steel with phosphorus and copperby cementation which consists in heating the metal under nonoxidizingconditions in contact with an oxygen compound of phosphorus, a salt ofcopper, and a catalyst at temperatures sufllcient to decompose thecompounds of phosphorus and copper.

8. The process of impregnating iron or steel ,with phosphorus bycementation which consists in heating the metal under non-oxidizingconditions in contact with an oxygen compound of phosphorus and acatalyst at a temperature sumcient to decompose the phosphorus compound.

9. The process of impregnating iron or steel with phosphorus bycementation which consists in heating the metal under non-oxidizingconditions in contact with phosphorus pentoxide at a temperaturesufllcient to decompose the phosphorus pentoxide.

10. The process of .impregnating with phosphorus and copper bycementation a metal capable oi! alloying with phosphorus and copperwhich consists in heating the metal under nonoxidizing conditions incontact with an OXYBGn compound of phosphorus and an organic salt ofcopper at temperatures sufilcient to decompose the compounds ofphosphorus and copper.

11. The process of impregnating with phosphorus and copper bycementation a metal capable of alloying with phosphorus and copper whichconsists in heating the metal under nonoxidizing conditions in contactwith a copper salt at a temperature suflicient to decompose the coppersalt, and thereafter heating the metal under the same conditions incontact with an oxygen compound of phosphorus at a temperaturesufficient to decompose the phosphorus compound.

12. A cementation compound for the treatment of iron or steel to providethe latter with a non-oxidizing and corrosion-resisting case, consistingof an oxygen compound of phosphorus, and a catalyst.

13. A cementation compound for the treatment of iron or steel to providethe latter with a non-oxidizing, corrosionand acid-resisting cementationcase, consisting of an organic salt of copper, and an oxygen compound ofphosphorus.

14. A cementation compound for the treatment oi iron or steel to providethe latter with a non-oxidizing, corrosionand acid-resisting cementationcase, consisting of an organic salt of copper, an oxygen compound ofphosphorus, finely divided silica, and a catalyst.

15. The process or impregnating iron or steel with phosphorus and copperby cementation which consists in heating the metal under non-- oxidizingconditions in contact with an oxygen compound'oi! phosphorus, finelydivided silica,

and a copper salt in an iron container at temperatures suflicient todecompose the phosphorus and copper compounds.

16. The process 01' impregnating iron or steel with phosphorus andcopper by cementation which consists in heating the metal undernonoxidizing conditions in contact with an oxygen compound ofphosphorus, finely divided silica, and nickel oxalate in a closedcontainer at temperatures sumcient to decompose the phosphorus compound.

17. The process of impregnating iron or steel with phosphorus bycementation which consists in heating the metal under non-oxidizingconditions in contact with an oxygen compound of phosphorus and finelydivided nickel at a temperature sumcient to decompose the phosphoruscompound.

18. The process of impregnating iron or steel with phosphorus bycementation which consists in heating the metal under non-oxidizingconditions in contact with an oxygen compound of phosphorus in an ironcontainer at a temperature suiiicient to decompose the phosphoruscompound.

l9. The process of impregnating'iron or steel with phosphorus bycementation which consists in heating the metal under non-oxidizingconditions in contact with an oxygen compound of phosphorus and silicaat a temperature sumcient to decompose the phosphorus compound.

20. The process of impregnating with phosphorus by cementation a metalcapable of alloying with phosphorus which consists in heating the metalin contact with an oxygen compound of phosphorus, and finely dividedcarbon in a nitrogen atmosphere at a temperature sufllcient to decomposethe phosphorus compound".

21. The process of impregnating with phosphorus by cementation a metalcapable of alloying with phosphorus which consists in heating the metalin contact with an oxygen compound of phosphorus in an atmosphere ofcity gas at a temperature sutllcient to decompose the phosphoruscompound.

22. The process of impregnating with phosphorus by cementation a metalcapable of alloying with phosphorus which consists in heating the metalin contact with an oxygen compound of phosphorus in an atmosphere ofcity gas and nitrogen at a temperature suflicient to decompose thephosphorus compound.

23. The process of impregnating iron or steel with phosphorus and copperby cementation which consists in heating the metal under nonoxidizingconditions in contact wtih oxides of phosphorus and copper attemperatures sufflcient to decompose the oxides of phosphorus andcopper.

24. The process of impregnating iron or steel with phosphorus and copperby cementation which consists in heating the metal under nonoxidizingconditions in contact with oxides of phosphorus and copper attemperatures suiiicient to decompose the oxides of phosphorus andcopper, and in the presence of a catalyst.

25. A cementation compound for the treatment of iron or steel to providethe latter with a nonoxidizing, corrosion and acid resisting cementationcase consisting of an oxygen compound of phcsphomasilica, and an oxideof copper.

26. As a new article of manufacture, iron or steel having a cementationcase containing phosphorus and copper made in accordance with theprocess described in claim 2.

27-. As a new article of manufacture, iron or steel having a cementationcase containing phosphorus and copper made in accordance with theprocess described in claim 4.

28. As a new article of manufacture. iron or steel having a copper ironcore and a copper phosphorus iron cementation case made in accordancewith the process described in claim 5% 29. As a new article ofmanufacture, a cop.- per bearing steel having a cementation casecontaining phosphorus or a compound of phosphorus made in accordancewith the process described in claim 5.

HARRY K. IHRIG.

